A compound existential risk (also known as a combination existential risk (Brennan 2019) and as an intermediate existential risk (Ćirković, Sandberg & Bostrom 2010)) is an existential risk arising from two or more distinct event types.

Owen Cotton-Barratt, Max Daniel and Anders Sandberg illustrate the concept of a (non-existential) compound risk with the following historical incident (Cotton-Barratt, Daniel & Sandberg 2020: 279):

the deadliest accident in aviation history occurred when two planes collided on an airport runway; this was only possible because a previous terrorist attack on another airport had caused congestion due to rerouted planes, which disabled the prevention measure of using separate routes for taxiing and takeoff.

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